hdu 4741

今天的比赛前面四个多小时没有出题，智商真是拙计；

其实前面都是水题，就是想不到思路！

知道最后40分钟，和小珺同志把这个计算几何的题给A了；

然后小琪也马上把第3题干掉了；

代码：

#include<cstdio>
#include<cstring>
#include<cmath>
using namespace std;
struct point3
{
    double x,y,z;
};

//向量大小
double vlen(point3 p)
{
    return sqrt(p.x*p.x+p.y*p.y+p.z*p.z);
}

//计算 dot product U . V
double dmult(point3 u,point3 v)
{
    return u.x*v.x+u.y*v.y+u.z*v.z;
}

//计算 cross product U x V
point3 xmult(point3 u,point3 v)
{
    point3 ret;
    ret.x=u.y*v.z-v.y*u.z;
    ret.y=u.z*v.x-u.x*v.z;
    ret.z=u.x*v.y-u.y*v.x;
    return ret;
}
//矢量差 U - V
point3 subt(point3 u,point3 v)
{
    point3 ret;
    ret.x=u.x-v.x;
    ret.y=u.y-v.y;
    ret.z=u.z-v.z;
    return ret;
}

point3 intersection(point3 u1,point3 u2,point3 v1,point3 v2)
{
    point3 ret=u1;
    double t=((u1.x-v1.x)*(v1.y-v2.y)-(u1.y-v1.y)*(v1.x-v2.x))
             /((u1.x-u2.x)*(v1.y-v2.y)-(u1.y-u2.y)*(v1.x-v2.x));
    ret.x+=(u2.x-u1.x)*t;
    ret.y+=(u2.y-u1.y)*t;
    ret.z+=(u2.z-u1.z)*t;
    printf("%0.6lf %0.6lf %0.6lf ",ret.x,ret.y,ret.z);
    return ret;
}

double linetoline(point3 u1,point3 u2,point3 v1,point3 v2)
{
    point3 a=subt(u1,u2);
    point3 b=subt(v1,v2);

    //point3 ans=intersection(u1,u2,a,b);
    point3 n=xmult(a,b);
    return fabs(dmult(subt(u1,v1),n))/vlen(n);
}

point3 add(point3 a,point3 b)
{
    point3 ret;
    ret.x=a.x+b.x;
    ret.y=a.y+b.y;
    ret.z=a.z+b.z;
    return ret;
}

int main()
{
    point3 a,b,c,d;
    int t;
    scanf("%d",&t);
    while(t--)
    {
        scanf("%lf%lf%lf",&a.x,&a.y,&a.z);
        scanf("%lf%lf%lf",&b.x,&b.y,&b.z);
        scanf("%lf%lf%lf",&c.x,&c.y,&c.z);
        scanf("%lf%lf%lf",&d.x,&d.y,&d.z);
        printf("%.6lf
",linetoline(a,b,c,d));
        point3 x1=subt(a,b);
        point3 x2=subt(c,d);
        point3 n=xmult(x1,x2);
        double k=d.x-c.x;//kk:k k:K
        double l=d.y-c.y;
        double m=d.z-c.z;
        double h=b.x-a.x;
        double i=b.y-a.y;
        double j=b.z-a.z;
        double N=h*i*l-i*i*k-j*j*k+h*j*m;
        double O=h*h*l-h*i*k-i*j*m+j*j*l;
        double P=h*j*k-h*h*m-i*i*m+i*j*l;
        double Q=-a.x*N+a.y*O-a.z*P;
        double kk=(O*c.y-N*c.x-P*c.z-Q)/(N*k-O*l+P*m);
        point3 ss;
        ss.x=k*kk+c.x;
        ss.y=l*kk+c.y;
        ss.z=m*kk+c.z;
        point3 ans=intersection(ss,add(ss,n),a,b);
        printf("%.6lf %.6lf %.6lf
",k*kk+c.x,l*kk+c.y,m*kk+c.z);
    }
    return 0;
}